As in Nana's Birthday Party , Hest fashions tender, intimate relationships between children and their grandparents. But this title's meager plot and uncharacteristically awkward prose overshadow Hest's natural warmth as a storyteller. Ruby packs a basket of cookies and checkers for a visit to Grampa's. But Ruby must walk through a spring storm to get there. After savoring the storm's power and its effects (``the greengrocer chased apples and pears''), she finally arrives at Grampa's to spend a cozy evening. Although Grampa and Ruby's hot chocolate party brings a satisfying denouement, the story suffers from distractions ranging from odd similes and images (``the city looked like night'' and ``windows shot down'') to such non sequiturs as Ruby's daydream of having a dog accompany her to Grampa's. This book's silver lining, however, lies in Cote's childlike gouaches. Ebullient and pleasingly off-kilter, they convey Ruby's sense of adventure and the slightly wild glee of a romp in the rain. Ages 4-7. (Mar.)